266 THE SCHOOL OF RifiAUMUR 



which possess a true organ of voice ; the sounds which 



they emit are always due to vibration or friction. In 



this case the wings take no part in the production of the 



sound, for when they are held the sound does not cease, 



but becomes louder than before. It seems to proceed 



from the head of the moth. Reaumur satisfied himself 



that it was due to the rubbing of the palps against the 



proboscis. When the proboscis was forcibly extended 



with a pin, the sound ceased altogether; when only 



one of the palps was allowed to act the sound was 



weakened. 



The Blow-fly 



Reaumur describes with careful detail the external 

 features of the winged blow-fly. Among other things 

 he discusses the mechanism which enables the feet to 

 adhere even to a vertical glass surface, though without 

 remarking the exudation which is now known to be 

 essential. The eyes, simple and compound, the balancers 

 (halteres), and the membranes by which they are covered 

 in certain flies, the spiracles, and the air-reservoirs all 

 receive careful consideration. He gives an elaborate 

 account of the proboscis, and compares it with that of a 

 moth.^ He is not satisfied with an enumeration of the 

 parts ; he must show them in action. His method of 

 study was to smear the inside of a glass vessel with 

 syrup, introduce some flies, and then watch them with a 

 lens. He saw the terminal disk applied to the sugared 

 surface in a hundred changing attitudes, expanded or 

 contracted, pressed flat, inclined, or hollowed into a 

 funnel ; he saw undulations travelling along the grooves, 

 liquid sucked up the tubular stem, and now and then an 

 outflow of saliva (made more evident by bubbles of air), 

 which served to dilute the syrup. 



1 Vol. IV, Mem. v. 



